These are my recommendations of who to follow and what happens when with educational discussions. Twitter is a fantastic forum for not just free expression but for professional development, pedagogical discussion and planning. If you pick who and what you follow carefully it can be like a staffroom, just for maths teachers, thousands of maths teachers and its on your sofa!
#mathsTLP Teacher Lesson Planning for maths teachers Sundays 7-8
#mathschat Maths teaching discussion and a general hashtag for throughout the week. Discussions Wednesdays at 8
#ukedchat Not maths specific but a good chat Thursdays at 8